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REGIONAL VARIATIONS IN SOURCE ROCK MATURATION IN THE LUSITANIAN BASIN (PORTUGAL) – THE ROLE OF RIFT EVENTS, SUBSIDENCE, SEDIMENTATION RATE, UPLIFT AND EROSION

Third Central & North Atlantic Conjugate Margins Conference
Trinity College Dublin, 22-24 August 2012
Abstracts Volume Page 91
REGIONAL VARIATIONS IN SOURCE ROCK MATURATION IN THE LUSIT ANIAN BASIN
(PORTUGAL) THE ROLE OF RIFT EVENTS, SUBSIDENCE, SEDIMENTATION RATE, UPLIFT AND
EROSION
Bernardo A. Teixeira1, Nuno Pimentel1 & Rui Pena dos Reis2
1 Centro de Geologia, Lisbon University BernardoAlmeidaFcul@gmail.com Pimentel@fc.ul.pt
2 Centro de Geociências, Coimbra University PenaReis@dct.uc.pt
The Lusitanian Basin developed in the Mesozoic in the western Iberia margin (Figures 2A and
2B) and comprises sediments from the Late Triassic to Cretaceous (Pena dos Reis et al.,
2010). Its evolution has close relations with the opening of the North Atlantic, as well as the
opening and closure of the Western Tethys. Two main rift phases are classically considered,
and have been used for modelling, in Late Triassic (229-199 Ma) and Late Jurassic (159-140
Ma). The total thickness of the Mesozoic infill is up to 5 km, mainly of Jurassic age, locally
covered by Tertiary basins related with alpine inversion (Stapel et al., 1996). Three sectors
may be defined (North, Central and South), separated by major NE-SW faults - Nazaré and
Tagus Valley. The Central sector presents the main depocenter of the basin, with three sub-
basins (Turcifal, Bombarral and Arruda) developed in Upper Jurassic times.
The main intervals with hydrocarbon generating potential are Lower Jurassic (Água de
Madeiros and Vale das Fontes Formations) and Upper Jurassic (Cabaços/Vale Verde
Formation). The Upper Jurassic interval is geochemically more variable, but presents better
TOCs and HIs basin-wide, with higher net thickness for hydrocarbon generation, than the
Lower Jurassic units (see Teixeira, 2012).
Ten oil exploration wells have been analysed along the basin, regarding thickness and age of
its sedimentary infill (Teixeira, 2012). Maturation evaluation was based in the PetroMod 1D
software from IES Schlumberger (Figure 1). Backstripping of wells allowed to infer tectonic
subsidence and to estimate stretching factors (Beta) of each of the two rift phases. Beta
values were used to model heat flow in each rift phase. Sedimentation rates were evaluated,
in order to identify large sedimentary input periods in the basin, associated with rifting phases.
For the first rift phase (Upper Triassic), stretching factors are higher in the northern sector
(~1.05 1.18), as well as in the offshore and the Turcifal sub-basin of Central sector (~1.09
1.19). For the second rift phase (Upper Jurassic), stretching factors are higher in the
Bombarral and Arruda sub-basins of the Central sector (~1.11 1.19) and in the Southern
sector (~1.06 1.09).
According to PetroMod modelling (Teixeira, 2012), the main factor controlling and ruling the
maturation evolution in the Lusitanian Basin is the heat flow increase, induced by the Late
Triassic and Late Jurassic rift phases (Figure 1). Secondary factors, yet extremely important
are: a) North sector - Cretaceous infill, prior to Aptian uplift and erosion; b) Central sector -
high Upper Jurassic sedimentation rates, mainly induced by the sub-basins tectonics; c)
South sector - high Cenozoic sedimentation rates, in times with low heat-flow, may explain
maturation (more wells need to be studied).
Lower Jurassic source rocks are mature, for oil or gas, in all the three sectors of the
Lusitanian Basin, while Upper Jurassic source rocks are only mature in the Central sector, for
oil, being immature in the other two sectors (Figures 2C and 2D).
These data need to be integrated with other regional data, such as source-rock thicknesses
and palaeogeographic and organic content variations, in order to establish a robust and
predictive exploration tool. This approach may be extended to other western Iberian basins,
such as the Peniche and Alentejo, both offshore and a few hundred kilometres apart.
Third Central & North Atlantic Conjugate Margins Conference
Trinity College Dublin, 22-24 August 2012
Abstracts Volume Page 92
References:
Matos, V.G.A.E. 2009. Estudo de palynofácies e de fácies organic de uma sequência sedimentary do
Jurássico inferior da Bacia Lusitânica. Master thesis, Departmento de Ciências da Terra da Faculdade
de Ciências e Technologia da Universidade de Coimbra, 108 pp. (unpubl.)
Pena dos Reis, R., Pimentel, N., Garcia, A.J.V., Viana, A., & Bueno, G. 2010. Mesozoic subsidence
and uplift history of an exposed Atlantic rifting margin the Lusitanian basin (Portugal). II Central &
North Atlantic Conjugate Margins, Lisbon 2010, Extended Abstracts, 74.
http://metododirecto.pt/CM2010/index.php/vol/article/view/235
Stapel, G., Cloetingh, S. & Pronk, B. 1996. Quantitative subsidence analysis of the Mesozoic evolution
of the Lusitanian Basin (western Iberia margin). Tectonophysics, 266, 493-507.
Teixeira, B.A. 2012. Modelação da subsidência, evolução térmica e maturação de intervalos
geraDorés do Jurássico na Bacia Lusitânica. MSc Thesis, Universidade de Lisboa, (unpubl.)
Third Central & North Atlantic Conjugate Margins Conference
Trinity College Dublin, 22-24 August 2012
Abstracts Volume Page 93
Figures 2A & 2B: Lusitanian Basin location (green), main structures and Sectors (in Matos, 2009).
Figures 2C & 2D: Hydrocarbon maturation in the studied wells.
Figure
1: PetroMod model
ling of hydrocarbon
maturation in three selected wells. A
Vm-
1
(North Sector) showing Lower Jurassic in “oil
window” and Upper Jurassic “immature”. B
Cp
-1 (Central Sector) showin
g Lower Jurassic
in “wet gas window” and Upper Jurassic in
“late oil window”. C
Br-3 (South Sector)
showing Upper Jurassic “immature”.
A
C
C

Supplementary resource (1)

... Non-mature Lower Jurassic source-rocks are known in outcrop, namely at the Peniche, Montemor-o-Velho, and São Pedro de Muel sections (Oliveira et al., 2006;Spigolon et al., 2011;Duarte et al., 2012), but preliminary maturation modelling may suggest that the units have reached maturity in several exploration wells in the basin (Teixeira et al., 2012(Teixeira et al., , 2014. These non-mature Late Jurassic source-rocks are also present in different outcrops, such as Cabo Mondego or Montejunto (Spigolon et al, 2011), whereas they reached the oil-window in nearby wells such as SB-1, FX-1 and CP-1 (Teixeira et al., 2012(Teixeira et al., , 2014. ...
... Non-mature Lower Jurassic source-rocks are known in outcrop, namely at the Peniche, Montemor-o-Velho, and São Pedro de Muel sections (Oliveira et al., 2006;Spigolon et al., 2011;Duarte et al., 2012), but preliminary maturation modelling may suggest that the units have reached maturity in several exploration wells in the basin (Teixeira et al., 2012(Teixeira et al., , 2014. These non-mature Late Jurassic source-rocks are also present in different outcrops, such as Cabo Mondego or Montejunto (Spigolon et al, 2011), whereas they reached the oil-window in nearby wells such as SB-1, FX-1 and CP-1 (Teixeira et al., 2012(Teixeira et al., , 2014. This situation points to a very important role of differential subsidence along the basin, both in time and space. ...
... This phase is responsible for an increase in heat flow and, at the same time much overburden. In Downloaded from https://pubs.geoscienceworld.org/books/chapter-pdf/2617914/penapime.pdf by guest most places maturation has been attained in the Late Jurassic (Kimmeridgian to Tithonian) and it has been most prominent in the Oxfordian depocenters, namely the Central Sector's sub-basins of Arruda, Bombarral, and Freixial (Teixeira et al., 2012(Teixeira et al., , 2014. ...
... In nearby wells (e.g. SB-1, Pw-4, Fx-1 and CP-1; see Fig. 3 for locations), the presence of oil shows together with thermal modelling indicate oil-window maturities (Teixeira et al., 2012) (Fig. 9). ...
... In general, vitrinite reflectance data (BEICIP, 1996) and thermal modelling studies (Teixeira et al., 2012) suggest that the Lower Jurassic source rocks are mature for oil in the north of the Lusitanian Basin and mature for gas in the centre; whereas Upper Jurassic source rocks are mostly mature in the centre but not in the north. This difference is due to the influence of the thick, Late Jurassic synrift siliciclastics in depocentres in the central part of the basin (Teixeira et al., 2012). ...
... In general, vitrinite reflectance data (BEICIP, 1996) and thermal modelling studies (Teixeira et al., 2012) suggest that the Lower Jurassic source rocks are mature for oil in the north of the Lusitanian Basin and mature for gas in the centre; whereas Upper Jurassic source rocks are mostly mature in the centre but not in the north. This difference is due to the influence of the thick, Late Jurassic synrift siliciclastics in depocentres in the central part of the basin (Teixeira et al., 2012). However, the Lower Jurassic source rocks may locally be mature in depocentres to the north, for example around São Pedro de Muel (McWhorter et al., 2014). ...
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The relatively well-studied Lusitanian Basin in coastal west-central Portugal can be used as an analogue for the less well-known Peniche Basin in the deep offshore. In this paper the Lusitanian Basin is reviewed in terms of stratigraphy, sedimentology, evolution and petroleum systems. Data comes from published papers and technical reports as well as original research and field observations. The integration and interpretation of these data is used to build up an updated petroleum systems analysis of the basin. Petroleum systems elements include Palaeozoic and Mesozoic source rocks, siliciclastic and carbonate reservoir rocks, and Mesozoic and Tertiary seals. Traps are in general controlled by diapiric movement of Hettangian clays and evaporites during the Late Jurassic, Late Cretaceous and Late Miocene. Organic matter maturation, mainly due to Late Jurassic rift-related subsidence and burial, is described together with hydrocarbon migration and trapping. Three main petroleum systems may be defined, sourced respectively by Palaeozoic shales, Early Jurassic marly shales and Late Jurassic marls. These elements and systems can tentatively be extrapolated offshore into the deep-water Peniche Basin, where no exploration wells have so far been drilled. There are both similarities and differences between the Lusitanian and Peniche Basins, the differences being mainly related to the more distal position of the Peniche Basin and the later onset of the main rift phase which was accompanied by Early Cretaceous subsidence and burial. The main exploration risks are related to overburden and maturation timing versus trap formation associated both with diapiric movement of Hettangian salt and Cenozoic inversion. ON-LINE FULL VERSION http://onlinelibrary.wiley.com/doi/10.1111/jpg.12648/epdf
... Maturation of both source rocks has been modeled, based in lithology and thickness well data, calibrated by vitrinite reflectance data (Teixeira et al., 2012(Teixeira et al., , 2014. Both Jurassic source rocks have attained the hydrocarbon generation window, although not everywhere in the basin as a result of the highly heterogeneous basin's subsidence and overburden, especially in the Late Jurassic. ...
... Non-mature Lower Jurassic source rocks are known in outcrop, namely at the Peniche, Montemor-o-Velho and São Pedro de Muel sections (Oliveira et al., 2006;Silva et al., 2010;Spigolon et al., 2011;Duarte et al., 2012), but the same units have reached maturity in several exploration wells in the basin (Teixeira et al., 2012(Teixeira et al., , 2014. Also, non-mature Upper Jurassic sourcerocks are known in different outcrops, such as Cabo Mondego or Montejunto (Spigolon et al., 2011), whereas they reached the oil window in nearby wells such as SB-1, FX-1 and CP-1 (Teixeira et al., 2012(Teixeira et al., , 2014. ...
... Non-mature Lower Jurassic source rocks are known in outcrop, namely at the Peniche, Montemor-o-Velho and São Pedro de Muel sections (Oliveira et al., 2006;Silva et al., 2010;Spigolon et al., 2011;Duarte et al., 2012), but the same units have reached maturity in several exploration wells in the basin (Teixeira et al., 2012(Teixeira et al., , 2014. Also, non-mature Upper Jurassic sourcerocks are known in different outcrops, such as Cabo Mondego or Montejunto (Spigolon et al., 2011), whereas they reached the oil window in nearby wells such as SB-1, FX-1 and CP-1 (Teixeira et al., 2012(Teixeira et al., , 2014. This situation points to a very important role of differential subsidence along the basin, both in time and space. ...
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... Non-mature Lower Jurassic source-rocks are known in outcrop, namely at the Peniche, Montemor-o-Velho, and São Pedro de Muel sections (Oliveira et al., 2006;Spigolon et al., 2011;Duarte et al., 2012), but preliminary maturation modelling may suggest that the units have reached maturity in several exploration wells in the basin (Teixeira et al., 2012(Teixeira et al., , 2014. These non-mature Late Jurassic sourcerocks are also present in different outcrops, such as Cabo Mondego or Montejunto (Spigolon et al, 2011), whereas they reached the oil-window in nearby wells such as SB-1, FX-1 and CP-1 (Teixeira et al., 2012(Teixeira et al., , 2014. ...
... Non-mature Lower Jurassic source-rocks are known in outcrop, namely at the Peniche, Montemor-o-Velho, and São Pedro de Muel sections (Oliveira et al., 2006;Spigolon et al., 2011;Duarte et al., 2012), but preliminary maturation modelling may suggest that the units have reached maturity in several exploration wells in the basin (Teixeira et al., 2012(Teixeira et al., , 2014. These non-mature Late Jurassic sourcerocks are also present in different outcrops, such as Cabo Mondego or Montejunto (Spigolon et al, 2011), whereas they reached the oil-window in nearby wells such as SB-1, FX-1 and CP-1 (Teixeira et al., 2012(Teixeira et al., , 2014. This situation points to a very important role of differential subsidence along the basin, both in time and space. ...
... This phase is responsible for an increase in heat flow and, at the same time much overburden. In most places maturation has been attained in the Late Jurassic (Kimmeridgian to Tithonian) and it has been most prominent in the Oxfordian depocenters, namely the Central Sector's sub-basins of Arruda, Bombarral, and Freixial (Teixeira et al., 2012(Teixeira et al., , 2014. ...
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The Early Jurassic in the Lusitanian Basin is known from several outcrops, especially in its northernmost part, and they represent the initial phase of the basin carbonate infilling (Figs. 1, 2 and 3). The present work is focused on the study of the Água de Madeiros (upper Sinemurian) and the Vale das Fontes (Pliensbaquian) Formations (Fig. 2 and Fig. 3). This stratigraphic interval is characterized by a marly-calcareous sedimentation that resulted from a paleoenvironmental setting recognized in the evolution of the Lusitanian Basin, which is consistent with organic matter accumulation (Fig. 3 and Fig. 4). This works aims to reinforce the understanding about organic matter origin, decomposition, preservation, modification, distribution and incorporation in sediment. It also intends to identify the depositional trends of the particulate organic content and to analyse the palynofacies parameters, behaviour as well as the depositional settings related to the sediments that make up these litostratigraphic units. In order to do so, techniques were applied and put together for the first time in what concerns the sediments of the Early Jurassic of the Lusitanian Basin. These techniques comprise Palynofacies Analysis and Organogeochemical Analysis (Total Organic Carbon – TOC). Twenty nine outcrop samples were collected and laboratory processed for the palynofacies (thin sections) and organogeochemical analysis. For the palynofacies analysis, microscopic techniques were applied (transmitted white light microscopy and fluorescence microscopy), in which 300 organic particles were counted and a second counting method was associated that only comprised the palinomorph fraction of the total organic matter (associated counting). The organogeochemical analysis were used to quantify the Total Organic Carbon (COT) present in the samples. The percentage data obtained from counting of the kerogen groups and subgroups was statistically treated by cluster analysis, using Q-mode to determine groups of similar samples and R-mode to assess similarities between organic components. Furthermore, correlation matrices were calculated using the Pearson’s correlation coefficient r, which showed the links between organic components. The results showed that the amorphous organic matter group (A.O.M., Fig. 12 C, D, F and G) was predominant in the Água de Madeiros Formation (S. Pedro de Moel outcrop), followed by the phytoclast (Fig. 12 A, B) and the palynomorph groups, while in Vale das Fontes Formation (Coimbra, S. Pedro de Moel and Peniche outcrops) the phytoclast group was the most abundant of all three groups (Fig 5). It also showed that organic components with the same proximal-distal tendency had a positive correlation, while those with such an opposite trend had a negative or inverse correlation. The abundance of pollen particles of the Classopollis genera (Fig. C, D, F, G, H and I) identified in the data leads to the suggestion that the Água de Madeiros Formation was deposited in a climate that changed from warm to semi-arid to an arid climate, whereas the Vale das Fontes Formation was deposited in a setting that switched from a warm to semi-arid climate to a mild to subtropical climate. The organogeochemical analysis indicate that there is great variability in the COT content, which is directly related to relative sea level changes, continental influence, basin redox conditions and organic matter preservation (Table 1). The high content of insoluble residue and the type of organic matter found show that there was a strong continental influence during deposition (Table 1). The information acquired from the palynofacies and organogeochemical analysis and the cluster analysis (Fig. 6) allowed the compartmentalization of the studied sedimentary sections into palynofacies intervals, in other words, intervals with the same organic features and similar patterns of organic material supply (Fig 7). The organic facies of these intervals were determined and these results suggest that the Água de Madeiros Formation (predominant organic facies B-BC) developed in a warm to arid climate with higher organic matter preservation, in an anoxic and low energy setting, while the Vale das Fontes Formation (predominant organic facies C-CD) deposited in a more temperate to subtropical climate, in a higher energy oxic setting, with an increased supply of organic continental material and lower preservation of the organic matter (Fig. 8). The sedimentation of Água de Madeiros and Vale das Fontes Formations has an intermediate trend. According to the variation of percentage of palynomorphs the deposition was made in the marine environment (Federova, 1977 and Duringer & Doubinger, 1985), but near the coast and with a strong continental influence (Fig. 9). Integrating organogeochemical and palynofacies data has lead to the characterization of subenvironments and it shows that the identified paleoenvironments had changed from an oxic, highly proximal platform setting to a disoxic, proximal platform setting (deeper facies). This indicates that the S.Pedro de Moel region acted as a depocentric area throughout the latest Sinemurian and almost the entire Pliensbaquian (Fig 8 and Fig. 10). In this work, an hipothetical model is proposed to explain the deposition of the Vale das Fontes Formation. It presents a probable paleogeographic position for the source of the terrestrial organic material (Fig 11). This was essential to justify the proximal features of the organic matter found in sediments that in previous works were ascribed to distal settings. It is also proposed that the source area for the continental organic supply found in Vale das Fontes Formation at the Peniche and S. Pedro de Moel outcrops was located at the westernmost margin of the Lusitanian Basin, where organic deposition probably was already conditioned by the basement blocks that nowadays represent the Berlenga-Farilhões. On the other hand, it is suggested that the continental organic matter found in Vale das Fontes Formation of the Coimbra outcrop derived from the eastern margin of the basin.
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Quantitative subsidence analysis of 26 wells in the Lusitanian basin provides new constraints on the western Iberian Mesozoic passive margin development. Backstripped tectonic subsidence curves show a three-fold subdivision of vertical motions from Late Triassic onward. Continental rifting was initiated during the Late Triassic and Early Jurassic. From Middle Jurassic onward a distinct different behaviour is expressed in the subsidence curves for the North and the South Lusitanian basin. During the Middle Jurassic the South Lusitanian basin records a stretching episode with stretching factors of about 1.08, while the North Lusitanian basin typically has a Middle Jurassic hiatus. This different development is also expressed in the Late Jurassic and Early Cretaceous sedimentary sequence when both the North and South Lusitanian basin are subjected to another stretching episode, with a more pronounced development of the southern than of the northern part of the basin. The stretching factors for this last phase are about 1.03 for the northern part and 1.08 for the southern part of the area. This north-south difference during the Middle Jurassic to Early Cretaceous, for which the transition roughly coincides with the location of the Nazaré fault zone, is probably a result of differences in pre-rift crustal composition or thickness. Late Cretaceous sediments are mostly absent in the analysed wells. In the southern part of the basin the absence of the Cretaceous record is a consequence of erosion due to Cenozoic inversion of the basin. The generally low estimates for stretching factors suggest that the analysed eastern part of the Lusitanian basin forms the distal part of the mid-Cretaceous continental breakup. A comparison with subsidence curves of neighbouring basins of Iberia reflects general patterns in Mesozoic basin development and confirms the generally held view that the extension leading to continental breakup migrated from south to north during the Middle Jurassic to Early Cretaceous in West Iberia.
Mesozoic subsidence and uplift history of an exposed Atlantic rifting margin -the Lusitanian basin (Portugal). II Central & North Atlantic Conjugate Margins
  • R Pena Dos Reis
  • N Pimentel
  • A J V Garcia
  • A Viana
  • G Bueno
Pena dos Reis, R., Pimentel, N., Garcia, A.J.V., Viana, A., & Bueno, G. 2010. Mesozoic subsidence and uplift history of an exposed Atlantic rifting margin -the Lusitanian basin (Portugal). II Central & North Atlantic Conjugate Margins, Lisbon 2010, Extended Abstracts, 74. http://metododirecto.pt/CM2010/index.php/vol/article/view/235
Modelação da subsidência, evolução térmica e maturação de intervalos geraDorés do Jurássico na Bacia Lusitânica
  • B A Teixeira
Teixeira, B.A. 2012. Modelação da subsidência, evolução térmica e maturação de intervalos geraDorés do Jurássico na Bacia Lusitânica. MSc Thesis, Universidade de Lisboa, (unpubl.)